When handling liquids or gases at temperatures below an ambient or background temperature, special care should be taken to thermally insulate the ambient environment from the liquid or gaseous environment. Problems can arise from heat transfer between the liquid or gas environment through the containment material used to hold the liquid or gas. One such problem is that moisture within the ambient environment may be released from that environment and, if the temperature of the gas or liquid is low enough, that moisture may be frozen onto the surface of the containment material. Where moving parts are found within the containment material or where an interface exists between two detachable parts of the containment material, as is the case with nozzle attachments used to join lines for transferring liquid or gas between holding tanks, such parts can be difficult to move or detach, as the case may be, when moisture has frozen in and around those parts.
By way of example, such a problem arises where liquefied or cryogenic gases are being transferred between holding vessels. The ambient environment in this case is the surrounding air in which the transfer takes place. Generally, a nozzle will be used to connect lines leading between the holding tanks. Such a nozzle can include a coupling mechanism to connect onto a receiving line or conduit that, in turn, directs the liquefied gas into the holding tank. The coupling mechanism on the nozzle can include moving parts. Other moving parts can also be found on the nozzle such as flow controls and associated valves that regulate the movement of liquefied gas between holding tanks. During transfer of the cryogenic liquid through the nozzle, moisture found in the air surrounding and within the nozzle will freeze onto the surface of the nozzle as the nozzle is cooled well below the freezing point of the moisture. Equally, moisture that has seeped into the moving parts or abutting interfaces of the nozzle may freeze, thereby restricting movement of those moving parts. The moving parts in such a case may be “locked” frozen in position until the moisture is removed, melted, broken or otherwise dislodge from the surfaces in question.
As well, moisture frozen on the surface of the nozzle can melt between transfers and seep into the moving parts. This can create an accumulation of moisture on the surfaces of these parts over the course of several transfers. As more moisture accumulates, the time to melt the moisture and liberate the nozzle's moving parts can increase with subsequent fills.
As well, moisture can also seep into and between the mating surface or the “abutting interface” where the nozzle and receiving line meet. If this moisture then freezes on the surfaces that define this abutting interface and across the interface, it can be difficult to detach the nozzle from the receiving line. Ice accumulation may need to be broken or melted before the nozzle can be removed from the receiving line. For the purposes of this application, abutting interface will refer to areas between the nozzle and receiving line over which moisture can accumulate and freeze. An abutting interface seal is that part of abutting interface that provide any barrier between the ambient environment and the abutting interface.
For the purposes of this application, cryogenic temperatures are below −100° C.
One cryogenic operation that can experience the problems noted above arises when refueling natural gas powered vehicles that store their fuel in a liquefied form. Natural gas vehicles store fuel as either a compressed gas or liquefied gas chilled to cryogenic temperatures, known as liquefied natural gas (LNG). There are significant advantages to storing natural gas as a liquid over storage as a compressed gas. For example, an equivalent amount of gas can be stored as a liquid in a much smaller volume than is the case where the gas is stored under pressure. However, when refueling, liquid natural gas (LNG) must be transferred at very cold temperatures resulting in some of the problems noted above.
The majority of refueling nozzles used in refueling operations include moving parts as well as abutting interfaces between the nozzle and receiving line. As such, moisture from the air that freezes onto these surfaces must be dealt with between refueling operations.
These issues become more pressing as cryogenic storage of natural gas becomes more popular. More vehicles utilizing cryogenic natural gas will eventually result in the need to provide “assembly line” refueling operations. Already, fleet operations exist that benefit from an ability to fuel successive vehicles quickly. As such, freezing of moisture from the air onto any mechanical mating coupling can slow such refueling operations.
Currently, LNG refueling operators have a few options to deal with this problem. First, they can wait for the mating coupling and nozzle to warm allowing the moisture frozen around the coupling and interface with the receiving line to melt or re-evaporate before removing the nozzle for a subsequent refueling. Second, nitrogen, dry air or a similar dry gas or appropriate liquid can be used to clear moisture from around the nozzle's moving parts. Third, they can break the iced surfaces.
The first option requires a wait that can range between several minutes and several hours between consecutive refueling operations depending on the ambient conditions. The second option can be expensive as it requires significant volumes of gas or liquid, as the case may be, to effectively remove as much of the moisture from around the nozzle as possible so as to prevent further penetration of moisture into the nozzle occurs prior to or during subsequent refueling operations. Ideally, dry gas should be used throughout filling to ensure that moisture is inhibited from flowing into the moving parts. During filling, ice can accumulate on the surfaces of the nozzle and between consecutive fillings, some of that accumulated ice can melt and seep into the nozzle. Significant amounts of nitrogen are normally required to ensure that this does not happen. The third option causes stress to the moving parts and abutting interface. Over time these parts can be damaged prematurely and the interface can loose its seal and integrity. Alternatively, the parts can be engineered to mitigate the affect of stresses discussed, however, such design considerations can be expensive.
A fourth option for cold substance transfer generally is to use a de-icing solution. Most such solutions however, are ineffective at the temperatures used for LNG and other cryogens. For example, a de-icing solution such as ethylene glycol or propylene glycol is effective at temperatures to approximately −50° C.
Nozzle designs have also been developed with complicated integrated mechanisms wherein moving parts are insulated from moisture buildup. While these are workable, they are expensive solutions that require the replacement of industry-accepted nozzles and the associated fittings on the receiving line. Also, the insulating means around the moving parts in such nozzles are integrated into the nozzles. Therefore, the choices for insulating material can be limited. This material may need to be malleable at low temperatures to accommodate moving parts while also being durable as it can be difficult, expensive and time consuming to replace. In some cases, when this insulating material fails, it can be less time consuming and, therefore, more economical to replace the entire nozzle. Either way, the expense of this solution is significant.
The present technique provides an insulating boot to overcome the problems noted above. The present technique also provides a method of overcoming the above problems wherein a removable insulating boot is adapted to a nozzle prior to transfer of cryogenic liquids. As well, the present technique provides a method of insulating the abutting interface and moving parts including coupling mechanisms and flow control mechanisms while, at the same time, avoiding the problems noted above.